Electrophotographic printing apparatus may comprise an image forming drum upon which an image is developed and an intermediate transfer member for transferring the developed image to a substrate. The intermediate transfer member is a drum or belt comprising a blanket typically comprising a conducting layer underlying a release coating elastomer layer. To transfer the image, the intermediate transfer member is charged to a predetermined voltage to generate an electrical potential between the intermediate transfer member and the image-forming drum causing the charged ink particles or charged toner to be attracted to the intermediate transfer member.
The blankets of the intermediate transfer member deteriorate over time making it advantageous, on occasion, to replace the blanket to maintain the performance of the apparatus. However, different blankets can have different thickness of a top layer above the conducting layer, including for example the release coating. For example, the thickness of the top layer for different blankets has been known to vary by up to 6 μm. These variations in thickness can change the electrical resistance of the blanket thereby changing the electrical potential generated between the image forming member and the intermediate transfer member when the predetermined voltage is applied. Variations in electrical potential affect the proportion of ink particles transferred to the intermediate transfer member which in turn affects print quality.
Current apparatus reduce the deterioration in print quality through a process called color adjustment. In this process, the amount of ink particles used to develop the image on the image forming drum is increased such that the amount of ink particles transferred to the intermediate transfer member remains substantially the same even though the proportion of ink particles transferred to the intermediate transfer member is reduced. The remaining ink particles not transferred to the intermediate transfer member are cleaned from the image-forming drum and thrown away after being separated via filters from the carrier liquid.
This process of color adjustment results in significant amounts of ink particles being thrown away and restricts the lifetime of the filters.